大学英语：There has been a lot of explanations as to the causes of panic attacks.

　　6.There has been a lot of explanations as to the causes of panic attacks.

　　本句中的as to 意思是about(关于)，如：

　　1)John has been given no directions as to what to write. (没人对约翰说明该写什么。)

　　2)I have no doubt as to his honesty.(对他的诚实，我毫无疑问。)

　　3)I was asked my opinion as to why he refused our help.(对他为什么拒绝我们的帮助，我被要求发现见解。)